Art. XVIII. — The Heathcotian — a Pre-Ordovician Series 

 — and its Distribution in Victoria. 



By J. W. GREGORY, D.Sc, F.R.S. 



[Read 13tli November, 1902]. 

 [With Plates XXIII.-XXVI.]. 



PAGK. 



I. Introduction ------- 148. 



II. Previous Literature ------ 149. 



III. The Geological Sequence at Heathcote — 



(A) Silurian - - - - - - - 152. 



(B) Ordovician - - - - - - - 153. 



(C) The Fossils of the Dinesus ida beds ; Nota- 



saphus, a New Genus of Trilobites - - 154. 



(D) The Heathcotian Series - - - - 156. 

 IV. Petrography - - - - - - - - 157. 



V. Age of the Heathcotian Series — 



(A) Relations with the Silurians - - - 160. 



(B) Relations with the Ordovicians - - - 161. 



(C) Geological Sequence at Heathcote - - 163. 

 VI. The Distribution of the Heathcotian Series in Victoria 164. 



VII. Relations of the Ordovician and Silurian Systems - 167. 



VIII. Subdivision of the Silurian System - - - 170. 



IX. Summary of Conclusions . . - . . 173. 



I. — Introduction. 



One of the most interesting and instructive rock series in 

 Victoria occurs along the floor of the Heathcote Valley, and 

 forms the crest of the Colbinabbin Range. Conflicting opinions 

 have been expressed as to the age and character of these rocks. 

 Several visits to diff'erent parts of the outcrop of the rocks 

 suggested to me a solution, which promised, to some extent, to 

 reconcile the views as to their interpretation. I have recently 

 been able to test this idea during a four days' visit to Heathcote 

 Avith my assistants, Messrs. H. J. Grayson and D. J. Mahony, 



